1. Technical Field
This invention relates generally to high performance flexible electrical cables and their manufacture, and more particularly to a flat cable having a high strength core element.
2. Background Art
High performance flexible electrical cables suitable for use in computer and similar high density cabling systems have heretofore been prone to the development of short circuits between the signal and the reference, or ground, planes. In an attempt to avoid this problem, many cables of this type arrange signal and ground conductors in coplanar, or side-by-side, relationship. For example, U.S. Pat. No. 4,783,293 issued May 31, 1988 to Kikuchi et al describes a flexible cable construction in which signal conductors are planarly arranged with reference, or ground, conductors which are in an exposed position after fabrication of the cable. U.S. Pat. No. 4,798,918 issued Jan. 17, 1989 to Kabadi et al describes an adhesively laminated structure having two parallel coplanar arrays consisting of adjacently positioned signal and ground conductors within each plane. When reference, or ground, conductors are arranged in side-by-side relationship with signal conductors, it decreases the number of signal conductors that can be carried within a fixed cable width at a required pitch, or lateral spacing. For example, only one-third of the conductors in the Kabadi et al arrangement can be used as signal conductors. Also, the Kabadi et al arrangement requires the use of a thin adhesive layer to bond adjacent layers of the cable. The use of adhesive materials in high performance flexible cable construction is generally undesirable because of the extra fabrication steps required to coat a substrate and cure the adhesive material. Also, adhesives generally cannot be used in the fabrication of cable assemblies that may be subsequently subjected to high temperature processing that may be required for high performance dielectric materials.
The present invention is directed to overcoming the problems set forth above. It is desirable to have a high performance flexible cable in which a plurality of signal conductors may be arranged in a plane at a fine pitch spacing without the requirement for ground conductors between adjacent conductors. It is also desirable to have such a flexible cable in which each of the planarly disposed signal conductors are in close proximity to a ground plane. It is also desirable to have such a flexible cable in which signal conductors may be disposed in two parallel planes with a ground plane positioned between the two parallel planes of signal conductors. Further, it is desirable to have such a flexible cable which has a core member which has high mechanical strength to provide improved mechanical integrity to the cable. Still further, it is desirable to have such a flexible cable construction, and a method of manufacturing such a cable, that does not use adhesive materials to bond adjacently disposed layers of conductors and dielectric material.